Bohnsack (also known as Bąsak; now known as Sobieszewo Island or Wyspa Sobieszewska; coordinates: 54.336389, 18.874722 [54° 20′ 11″ N, 18° 52′ 29″ E]; population in 1905, 928; in 2013, 3,570) is an island on the Baltic sea, located between the Gdańsk Bay and the delta of Vistula River. The island is the part of territory of the city of Gdańsk (formerly Danzig), Poland. The northern border of the island is the waters of Gdańsk Bay, while its southern border is a branch of the Vistula River, called Leniwka.

Until 1793 Bohnsack was part of Danzig in Royal Prussia (also known as Polish Prussia) in the Kingdom of Poland. The Second Partition of Poland in 1793 added Danzig and its surrounding territory to the province of West Prussia. Bohnsack was situated in the district (Kreis) of Danzig from 1818 until 1887, when it became part of the district of Danziger Niederung. The village became part of the Free City of Danzig from 1920 until the outbreak of World War II in 1939, when it came under the control of Nazi Germany. In February 1945 it was occupied by Soviet forces and eventually returned to Poland. In 2013 Bohnsack (now known as Sobieszewo Island) was one of the 30 quarters of Gdańsk.

Bohnsack was the location of the inn and cafe owned by Jakob Höppner, one of two Prussian delegates commissioned by Mennonites to visit South Russia in 1787-1788 in search of land for a new settlement.

There are no Mennonites listed in Bohnsack in the 1793 and 1820 records.